1. Field of the Invention
The present invention relates to a drafting means for a textile machine, more particularly to a device for loading a top roller on a bottom roller of a drafting means provided in a textile machine such as a spinning frame or roving frame.
2. Description of the Prior Art
The so-called roller drafting system is widely utilized for textile machines, especially in spinning machines. In the roller drafting system, a plurality of pairs of top and bottom rollers are arranged in such a manner that each downstream pair has a larger peripheral speed than the upstream pair. A fiber bundle such as a sliver or roving is advanced in the downstream direction while nipped between each top and bottom rollers. There, the bundle is attenuated between each adjacent pairs in accordance with the difference between their peripheral speeds.
In the most popular arrangement of spinning machines, a plurality of spinning stations, each comprising a drafting means, are arranged parallel to each other on the machine frame. Each drafting means comprises three bottom rollers, namely, front, middle, and back rollers, common to all of the spinning stations, and, on the front bottom roller, a front top roller, which comprises a set with the front top roller of an adjacent spinning station. The two front top rollers of each set are rotatably supported on a common shaft. The shaft is held by a single loading unit which exerts a loading force on the midportion of the shaft so that the set of top rollers is urged onto the bottom roller. The middle and back rollers each also has a loading unit of the same construction as that of the front top rollers. All the loading units are incorporated in one weighting arm.
A drawback of the above prior art is that the common shaft for the two top rollers of each set tends to incline relative to the axis of the bottom roller when one of the top rollers is forcibly detached from the bottom roller, which state often occurs when the fiber bundle is accidentally wrapped around the periphery of the top or bottom roller or when the widthwise thickness of the fiber bundle varies. This causes a change in the widthwise distribution of the loading force on the other side of the bottom roller and, therefore, the normal drafting operation of this drafting means is disturbed. In addition, since the loading units for each bottom roller are incorporated in one weighting arm, irregular displacement of one top roller influences all the other loading units, aggravating the draft unevenness.
Besides the above problem, particularly in a fasciated yarn spinning system, a top roller in the leading position of a drafting means, namely, a front top roller, has to be positively detached from a front bottom roller when the yarn piecing operation is carried out so as to reversely introduced a yarn end to be pieced into a drafting zone (for example, refer to Japanese Patent Application Nos. 58-65605, 58-52509, 58-52508, and 58-187696). In this case, of course, the drafting operation of the adjacent spinning station is disturbed so far as the conventional loading device is utilized. Therefore, it is strongly desired to provide a loading device in which each top roller in a weighting arm is displaceable without disturbing the operation of the adjacent spinning station.